This invention relates to a photo-electro-magnetic disc device.
In a photo-electro-magnetic disc device, data are recorded by locally heating a selected region with a spot of light while a magnetic field is applied to that local region, causing the magnetization of the local region to be orientated in the direction of the magnetic field.
A conventional photo-electro-magnetic disc device is illustrated in FIG. 1, wherein the photo-electromagnetic disc 1 is accommodated in a disc cartridge 2, and the disc 1 and the cartridge 2 are loaded, as one unit, in the device body. The cartridge 2 thus loaded is held by a cartridge holder 3. The cartridge holder 3, with the aid of a loading mechanism (not shown), moves the disc cartridge 2 into the device body and places the photo-electro-magnetic disc 1 on a turn table (not shown). The device has an optical head 5 for applying the light spot through an objective lens 4 to the photo-electro-magnetic disc 1 placed on the turn table, and magnetic field applying means 6 located on the side of the disc 1 which is opposite to the side facing the optical head 5. The magnetic field applying means 6 is made up of an E-shaped yoke 7 secured to the cartridge holder 3, and a coil 8 wound on the yoke 7. The magnetic field applying means 6 applies a magnetic field in predetermined direction to the part of the photo-electro-magnetic disc 1 to which the light spot is applied by the optical head 5. Further in FIG. 1, reference numeral 9 designates a frame.
The flow of magnetic flux formed by the magnetic field applying means 6 in the conventional device thus constructed extends from the center of the E-shaped yoke 7, and returns through the photo-electro-magnetic disc 1 to both ends of the E-shaped yoke 7. That is, as shown in FIG. 2, a magnetic circuit is formed substantially on one side of the photo-electro-magnetic disc 1. Therefore, the field strength may not be sufficiently high in the portions of the disc where the magnetic field need to be provided. Accordingly, in order to provide a sufficiently high magnetic field throughout the disc surface, it is necessary to provide a large coil and high power.